1. Field of the Invention
The present invention relates to a fluid-sealed anti-vibration device suitable for use in an engine mount for an automobile and the like.
2. Description of the Prior Art
A fluid-sealed anti-vibration device is known in the prior art wherein an elastic horizontal movable membrane is provided in a part of a side wall member which encloses a main fluid chamber to absorb the change of internal pressure in the main fluid chamber (one example, Japanese Unexamined Patent Publication No. Hei 10-281214).
Moreover, a fluid-sealed anti-vibration device is known in the prior art wherein an elastic membrane is formed as a circular member and the fluctuation of fluid pressure in a main fluid chamber can be absorbed by elastic deformation of the elastic membrane. The elastic membrane is integrally provided with a stopper projection serving as a circular wall. The stopper projection is formed on the surface of the elastic membrane on a sub-fluid chamber side. In the case of elastic deformation above a predetermined level, in particular, a spring constant is non-linearly changed by allowing the stopper projection to abut a partition member and the like.
In the case where such a horizontal movable membrane is provided, the dynamic spring constant can be generally lowered, but as shown by a dashed line in FIG. 6, a peak of the dynamic spring constant is in a medium frequency range. It is considered that this peak is generated as a reaction to the resonance of the horizontal movable membrane (the peak which is a maximum value of such a dynamic spring constant is hereinafter referred to as xe2x80x9cdynamic spring peakxe2x80x9d, while the minimum value is referred to as xe2x80x9cdynamic spring bottomxe2x80x9d).
It is an object of the present invention to control the resonance of a horizontal movable membrane so that generation of the dynamic spring peak can be controlled. In the present invention, a frequency below 500 Hz is defined as low frequency, a frequency between 100 and 500 Hz is defined as medium frequency, and a frequency above 500 Hz is defined as high frequency. In each graph in FIG. 6 and the like, the abscissa is the frequency, and the ordinate is the dynamic spring constant (absolute value of complex spring constant).
When an elastic membrane is provided in a partition member, there is a case where a circular elastic membrane can not be disposed due to layout conditions and must be changed to a non-circular member with a long side section and a short side section such as an oval shaped member. However, if the conventional circular elastic membrane is simply changed to a non-circular member such as that with an oval shape and the like, there is some possibility that the elastic membrane must be retained by the elastic membrane along the long side section for a long period of time, and since the stopper projection continues circularly, the elastic membrane can not be easily bent in response to the fluctuation of fluid pressure of a main fluid chamber. As a result, it is difficult to absorb the increase in the internal pressure. It is therefore an object of the present invention to provide an improved elastic membrane which can be easily bent in response to the fluctuation from increase in the internal pressure and absorb the increase in internal pressure even though the non-circular elastic membrane is used, in which when the elastic deformation exceeds a predetermined level, a spring constant can be changed non-linearly in the same manner as the prior art.
The primary object of the present invention is to overcome the above-mentioned problems and to provide a fluid-sealed anti-vibration device comprising a first connecting member secured to a source of vibration, a second connecting member secured to a car body, a substantially cone-shaped elastic body member positioned therebetween, a fluid chamber which is formed by the first connecting member, the second connecting member and the elastic body member, and of which the wall is a part of the elastic body member, the fluid chamber being divided by a partition wall into a main fluid chamber and a sub-fluid chamber, and an orifice provided in the partition wall to communicate with the main fluid chamber and the sub-fluid chamber, characterized in that an elastic horizontally movable membrane is formed in a side wall member which encloses the main fluid chamber in a substantially cylindrical manner, and a control wall is provided in the main fluid chamber to face the horizontally movable membrane at intervals.
According to a second object of the present invention, the horizontally movable membrane is integrally formed with the elastic body member. At this time, the control wall can be provided integrally with or separately from the partition member. Also, a plurality of horizontally movable membrane can be provided to allow the eigen value of each horizontally movable membrane to be changed.
According to a third object of the present invention, a circular wall is formed inside the side wall member to face the side wall member at intervals, space provided between the circular wall and the side wall member opens to the main fluid chamber, and a part of the circular wall facing the horizontally movable membrane is the control wall.
According to a fourth object of the present invention, an elastic membrane is provided on the partition member and adapted to be elastically deformed as a result of the fluctuation of internal pressure in the main fluid chamber, the elastic membrane is formed as a non-circular member with a long side section and a short side section and provided in the central part thereof with a curved groove running substantially parallel to the long side section.
At this time, on a surface of the elastic membrane opposite to the curved groove, a stopper projection is integrally provided substantially parallel to the curved groove. The stopper projection can be formed only on the long side section. The periphery of the elastic membrane is integrally formed with a continuous, circular peripheral wall that is retained by the partition member, and a clearance can also be provided at the retaining section by the partition member so as to permit deformation of the peripheral wall.
Further, the partition member is provided with first to third passages of which the first passage is the damping passage for always communicating with the main fluid and sub-fluid chambers, the second passage can be freely opened and closed, and the third passage, of which part is covered by the elastic membrane which is elastically deformable to shut off the communication with the main fluid and sub-fluid chambers, and the elastic membrane is formed as the non-circular member.
According to the first invention, because a control wall is provided to face a horizontally movable membrane, pressure on the horizontally movable membrane generated as a result of vibration of an elastic body member is controlled by the control wall and the dynamic spring constant is lowered by membrane resonance. As a result, generation of a dynamic spring peak generated in medium frequency range can be controlled.
As shown in FIGS. 5 and 6, formation of the dynamic spring peak can be freely controlled by changing the size of the control wall. Also, as shown in FIGS. 7 and 8, the dynamic spring peak can be controlled by changing the clearance between the horizontally movable membrane and the control wall. Accordingly, the fluid-sealed anti-vibration device can be regulated by changing the setting of the control wall.
According to the second invention, a plurality of horizontally movable membranes is provided, wherein if the eigen value of each membrane is changed, the resonance of each horizontally movable membrane is generated in different eigen values and coupled resonance which is wide as a whole is generated. As a result, a low dynamic spring effect can be realized in a wider range. In the present invention, the eigen value is defined as individual resonance frequency, which varies with the size, thickness, materials (spring constant) and the like of the horizontally movable membrane.
According to the third invention, since a circular wall is formed to face the side wall member, it is easy to position the control wall and the horizontally movable membrane.
According to the fourth invention, when the internal pressure of the main fluid chamber increases, the elastic membrane is sheared to bend and deform at the curved groove which is located in the center thereof and runs substantially parallel to the long side section, and which serves as a flexural center. In this manner, even though the elastic membrane is formed as the non-circular member with the long and short side sections, it can easily bend in response to the increase in the internal pressure in the main fluid chamber. As a result, it is possible to absorb the increase in internal pressure of the main fluid chamber by utilizing the low dynamic spring effect.
If the stopper projection is projectingly formed on a surface opposite to the curved groove of the non-circular member, when large vibrations are input to the main fluid chamber, the stopper projection abuts the side of the partition member, whereby the spring constant of the elastic membrane changes nonlinearly and, as a result, the large input can be absorbed. Further, by providing the stopper projection only on the long side section to provide a discontinuous shape, the elastic membrane can be easily bent.
Since the clearance is provided at the section where the partition member retains the peripheral wall of the elastic membrane, it is possible to realize easier deformation of the elastic membrane. Further, the partition member is provided with first to third passages, of which the first orifice passage is the damping orifice passage for always communicating with the main fluid and sub-fluid chambers, the second passage can be freely opened and closed, and the third passage, of which part is covered by the elastic membrane to shut off the communication with the main fluid and sub-fluid chambers. Thus, by forming the elastic membrane as the non-circular member, it is possible to provide an efficient layout even in such a limited space as that of the partition member where the circular member can not be positioned.